LAS VEGAS (AP) — Just 20 months ago, a former plumber from Dublin fought a fearsome superstar who hadn’t lost in a decade. Conor McGregor talked his way into a big-money showdown, but he had to back up his boasts against Jose Aldo, one of the greatest fighters in his sport.

McGregor finished the UFC featherweight champion in 13 seconds with one devastating left hand.

Floyd Mayweather presents an entirely different challenge when McGregor steps in the Vegas ring Saturday night. In his professional boxing debut, McGregor must figure out how to beat Mayweather at his own game — something the best boxers in the world have never done.

McGregor is a massive underdog, and deservedly so. But stop pretending the improbable doesn’t happen in combat sports, particularly when the self-proclaimed Mystic Mac is involved.

To declare McGregor can’t possibly win this fight displays more arrogance than, say, spending every night at a strip club the week beforehand, as Mayweather is currently doing.

Of course the hard-hitting Irishman has a chance — and there are several tactics he could employ to pull the biggest upset in boxing history.

“The people who don’t believe it don’t know anything about fighting,” said UFC President Dana White, who admittedly has a slight bias here. “This isn’t going to be a boxing match. This is going to be a fight.”

It’s also a fight between a 29-year-old southpaw in his prime and a 40 1/2-year-old veteran who hasn’t fought in nearly two years and doesn’t particularly want to be here, as he acknowledged repeatedly Wednesday. Mayweather isn’t the fighter he once was, and his competitive fire is dwarfed by his need for the mammoth paycheck from this endeavor.

But how does an MMA fighter with no competitive boxing experience since childhood take on a 21-year pro veteran with world championships in five divisions and arguably the most brilliant defensive skills in the history of the sport?

He gets in Mayweather’s face, both before and during the fight.

He charges forward from the opening bell and forces Mayweather to think defensively all night.

He throws hundreds of punches from every angle with the goal of setting up the vicious left hand that has turned out the lights on MMA opponents.

And if none of that is successful, McGregor could bend the Marquess of Queensberry rules to their breaking point in hopes of goading Mayweather into a brawl.

None of it is guaranteed to work. But it’s definitely worth a shot.

Looking back at Mayweather’s history is a daunting task, given his 49-0 record, but it contains clues for tactics that could magnify McGregor’s chances.

For instance, McGregor could amplify the strategy used by Marcos Maidana and Jose Luis Castillo. Both boxers pressed Mayweather constantly, using roughhouse tactics on the border of legality, and bombarded Mayweather with punches, many from unorthodox angles.

Mayweather won both fights, but definitely looked uncomfortable for long stretches. McGregor doesn’t have the hand speed of those professional boxers, but he should strive to emulate their urgency.

He should also attempt to show Mayweather things he’s never seen before in the ring, and his decision not to hire a boxing trainer for the bout might actually help in that regard. The UFC star should switch stances and try just about any punch, including the looping overhand shots rarely seen in high-level boxing matches because they’re easily countered, but common in MMA bouts because of the distance they create from the opponent.

If McGregor gets hit, so be it. Every punch absorbed is the price for a chance to reply.

McGregor believes Mayweather made a mistake by agreeing to fight in 8-ounce gloves instead of the typical 10-ounce pillows, but he shouldn’t rely solely on the unicorn one-punch knockout. While McGregor has definite power, only the biggest Mac homer would think it’s something Mayweather hasn’t seen from boxers — and Mayweather has shown a solid chin and excellent recovery skills on the few occasions he has been hit.

Instead, the key is to use that energy to get in a good position to unload the left hand or a combination through Mayweather’s shifty defense. McGregor could repeatedly tie up Mayweather and attempt to land shots in the clinch.

These things could all unsettle Mayweather, who typically doesn’t face trouble unless he takes a voluntary risk by moving into dangerous areas to throw combinations, or getting angry and brawling a bit.

And therein is another potential route for McGregor. Call it the Aldo Strategy: If he can get Mayweather feeling both confident and angry, there’s a chance Mayweather will let down his defense enough to attempt to finish McGregor in brute style — and maybe McGregor will have an opening.

Mayweather hasn’t seemed interested in McGregor’s typical trash talk during the buildup to the fight, but perhaps he could waver the champion’s focus with the wrong word, an errant elbow or a rabbit punch behind the head — enough to draw a warning, but not lose a point.

McGregor amplified his boasts this week, calling Mayweather “a broken man” and vowing to finish him within two rounds. Nobody knows whether McGregor actually believes his bluster, but the Irishman has defiantly vowed he will win.